Method and apparatus for separating materials of differing specific gravities



July 17, 1934. H, M. CHANCE 1,966,609

METHOD AND APPARATUS FOR SEPARATING MATERIALS OF DIFFERING SPECIFIC GRAVITIES Filed Dec. 15, 1932 InlJenfor Patented July 17, 1934 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR SEPARAT- ING MATERIALS F DIFFERING SPECIFIC GRAVITIES My invention relates to the separation of materials of differing specific gravities by the flotation of the lighter and sinking of the heavier in a separating fluid medium consisting of a maintained suspension in liquid of comminuted solids heavier than said liquid and substantially insoluble therein. Such separating mediums are described in United States Patents Nos. 1,224,138,

May 1, 1917, 1,462,881, July 24, 1923 and 1,561,909, November 17, 1925, in which such mediums are termed fluid masses.

In separating materials by such mediums, usually the liquid used is water and the comminuted solid a natural or manufactured sand.

My invention relates particularly tothe removal of comminuted solids from the lighter and from the heavier of said materials after separation thereof has been effected, also to the removal of fine particles of the lighter of said materials which tend to accumulate in said medium, and the cleaning of said comminuted solids by the removal therefrom of such contaminating material.

I will describe my invention as used in cleaning coal as this will enable those familiar with the art, to apply my invention to the separation of other materials, the concentration of ores, and the like.

The object of my invention is to increase the efliciency and reduce the cost of operating plants of the sand flotation process type by eliminating large sand sumps and sand pumps, by discharging the cleaned coal without removing therewith the solid constitutent of the separating medium, thus reducing breakage of coal and abrasion of screens.

In cleaning coal by this process as heretofore practiced a thin layer of coal floats at the top of the separating medium, through which the slate, rock and high-ash boney coal readily sink, the top of the separating medium being maintained at or above the overflow weir, so that a mixture of sand and water carries the coal through the weir, overlaid by an out-flowing stream of superposed water.

In my present invention the top of the separating medium is maintained at a considerable distance below the discharge weir, if such discharge weir be used, to prevent the discharge of sand with the coal, this being accomplished by reducing the quantity of separating medium used so that the top of said medium will be the desired distance below the weir or regionof discharge. Before feeding coal into said medium its top will be much lower than the working level of the top of said medium, because as coal with its intermixed refuse is fed into the medium, a corresponding quantity of fluid medium will be displaced upwardly until the quantity of coal and refuse designed to be maintained in the separator has been introduced.

The coal and admixed refuse is fed into the separator through internal or external feed conduit or conduits and discharged into, or falls by gravity to that part of the fluid medium which is to be used as the separating zone, and which may be adjacent to the level of said medium before coal and refuse is fed into it. The refuse falls to the lower part of said medium, while the coal rises and floats in that part of the medium above the separating zone.

As coal accumulates its buoyancy in the fluid medium causes the upper portion to be forced upwardly above the top of the fluid medium into the overlying body of water.

The quantity thus forced upwardly depends upon the quantity of submerged coal,'hence to secure large capacity the receptacle should accommodate several feet of submerged coal, providing buoyancy to support coal in the overlying water and also coal projecting above the top of the water line into the atmosphere.

While the apparatus shown by Fig. II is used to illustrate the separation of fine materials the flow of which may be controlled by a spigot, the apparatus may be used with feeders like those of Figs. I and II, or any type of feeder in common use for feeding coarse materials into the separator. The separator shown by this figure is cylindrical, and has a height or length greater than its diameter, so the floating material is a columnar mass, the height of which is greater than its diameter, but this or any other ratio of height to diameter is not essential to efficient functioning of the improvement, which requires only that there must be a sufficient vertical height to the separator to accommodate a quantity of floating material to raise by its buoyancy the upper layers of lighter material above the separating fluid mass and any liquid superposed thereon to discharge the lighter material into the atmosphere an appreciable distance above the water line.

With continued accretions of coal from the feed, the accumulated mass of coal and that supported above it will continually rise through and above the water and discharge into the air through a chute or weir provided for the purpose.

When upwardly rising water is used to maintain the separating zone and the medium below said zone at the desired specific gravity, the upward velocity of said water in said zone is much less than the falling velocity of the comminuted solid component or said medium, but in that portion containing the floating coal the upward velocity is doubled, because as about one-half of the area is occupied by submerged coal the water rises in the voids between the individual particles of coal at about twice its velocity in the separating zone, hence the spaciflc gravity of the medium in this upper zone is less than that in said separating zone.

This increased velocity produces more or less violent agitation of the accumulated coal and thus permits particles of the heavier materials that may have been carried up enmeshed with the floating lighter material, to fall therethrough to the lower part of the separating zone, in which primary separation was effected. The zone occupied by floating coal thus becomes a secondary separating zone of lower specific gravity than the primary zone upon which it is superposed.

If the upwardly rising liquid fails to produce sufiicient agitation of the submerged and supported coal, mechanical agitation such as revolving or other form of agitators may be used to prevent impacting of the floating coal in the region where the upward thrust from buoyancy of accumulated coal acts upwardly against the downward thrust due to the weight of the supported coal,- for this may cause binding against the walls of the separating receptacle and stop further upward movement thereof.

By increasing the fluidity and mobility of the accumulated materials agitation will greatly increase the capacity per unit of area, and also the eiiiciency of separation.

Such agitation will also insure the removal oi sand from the supported coal.

Water under pressure may be introduced into the supported coal above the top of the fluid medium, to assist in supporting the weight of the upper part of said supported coal, and by causing more rapid discharge of the clean coal will also cause more rapid rising of the submerged coal.

When the coal consist mainly of relatively large particles such as stove, egg or broken size, mechanical agitation may not be necessary, the up-. ward flowing water keeping the coal sufiiciently agitated to prevent the lumps from accumulating enough sand upon their upper surfaces to overcome their buoyancy; .further, when such lump does accumulate a considerable quantity of sand, it becomes top heavy, rolls over, the sand falls ofi, and thus produces agitation and jarring upon adjacent particles of coal which tends to free them from such sand accumulations.

As the specific gravity otthe fluid medium in the secondary separating zone is'less than that in the primary separating zone, it will not be sufficient to float all of the material floated by the primary zone, but the flotational effect produced 'by this lower specific gravity is aided by the impact of the rising current of liquid against the under surfaces of the particles of coal tending to push the particles upwardly and thus efiect an increase in the buoyancy of particles suspended in the medium. Hence we have in this zone the equivalent of classification by upwardly rising liquid acting jointly with buoyancy due to the fluid medium to effect the upward travel of all of the coal.

Further, this effect is doubtless increased more of said regions coacting to produce an upwardmovement carrying the coal to, through and above the body of superposed liquid to a discharge in the atmosphere above the top of said body of liquid.

The entire bodyoi upwardly rising coal is a single homogeneous mass of coal of uniform grade and free from stratiflcation with refuse or impure coal. If a few particles of refuse become aocidentally carried up by the coal, this condition is but momentary as such particles quickly begin to drop downward through the rising coal until they escape therefrom, and can therefore never become stratified in layers either above, within or below the body of rising coal, the specific gravity of the medium always being materially less than the specific gravity of such impure coal and refuse to insure the rapid fall therethrough of such heavier materials.

Proceeding now to a description of apparatus in which such process may be carried out.

In the drawing Fig. l is a vertical elevation and partly cross-sectional view of an apparatus for cleaning coal, or for separating other materials, concentrating ores and the like. Figure 11 is a similar elevation, partly in cross-section of an apparatus for removing fine particles of coal from sand, reconditioning sand for re-use and recovery by which water is clarified, and flne silt, coarse silt and sand free from coal are separately discharged.

In Figure I a cylindrical receptacle 1 diagrammatically shows a receptacle of any .desired shape, 2 is a downward extension of 1 of inverted truncated cone shape, which together with a portion of 1 is filled with fluid medium 3 of the described type. Valved water inlets are shown by d, and 5 is a weir for the discharge of water and coal. An agitator shaft 6 is provided with arms '7 located in 2, and arms 7 located in l. The shaft 6 is in operative relation to driving means comprising bevel gears and pulley 8.

Means for feeding coal into the separating zone 3 above the line CC are diagrammatically illustrated by coal pocket and chute 9, feed gate 10 and conduit 11, delivering the coal through an opening 12 in 1 into the separating zone.

. The line A--A marks the top of the water overlying the fluid medium 3, the line BIB the top of the fluid medium 3 before coal is introduced into 1, the line C-C the lower limit of the separating zone and the line B'B the top of the fluid medium when said medium above the separating zone is filled with coal floating therein, the water zone between B'B' and AA containing coal supported in said water zone by the buoyancy of coal floating below the line B'B'. The upper part of 1 is provided with valved inlet 13 for water above the line B'B to assist in supporting coal between B'B' and A-A and increase its rate of discharge through weir 5, into discharge chute 14 the bottom of which may be perforate and used as a dewatering screen.

Means for discharging the refuse are diagrammatically shown by an upper slide valve 15, refuse chamber 16, and lower slide valve 17, the valves 15 and 17 being operated by thrust cylinders 15 and 17, the piston rods of which are connected to the corresponding slide valve. The valves 15 and 17 are housed within the valve casings shown by the drawing. The refuse chamber 16 is provided with a valved inlet 18 for water to blow sand out of the interstices in the refuse prior to the discharge thereof, the sand passing through 15 to the fluid medium, and also to refill same after the discharge of refuse, and a valved air vent 19 for the escape of air.

Figure II has a receptacle 1 a downward extension 2', a fluid medium 3 filling 2' and 1' up to line B-B, valved means 4 for admitting water, a discharge weir 5', a revolving shaft 6', stirring arms '7 located in 2' and arms '7' located in 1'. The shaft 6' extends through the bottom of 2' to driving means illustrated by bevel gears and pulley 8, supported upon a ball bearing race 8a, the top of shaft 6 being carried by bearing 8b. Means for feeding thickened sand and coal silt into the zone above line 0-0 are shown by a thickener and spigot 9', valve 10 and a conduit 11'. The conduit 11' extends above 1' to the maximum height to which water can be forced by the pressure in 1 at the bottom of said conduit.

Sand free from the fine particles of coal is discharged with its water as fluid medium of the desired specific gravity by conduit 20, open at both top and bottom, through a discharge weir and chute 21. Weir 21 is at an elevation above the bottom of conduit 20 such that the weight of water, sand and silt in 1' above the open bottom of conduit 20, will cause the fluid medium to rise to and discharge through said weir.

Valved inlets for water are shown by 13. Weir 5' discharges coal silt, which may be recovered by dewatering screens.

Figure III is a modification of that part of Figure II above the line C-C in which a dilute mixture of sand, water and fine particles of coal may be fed into the region above the line B'-B' by a conduit or conduits 11".

The overflow from 1'' is through a weir or weirs at the top, a preferred type using practically the whole periphery of the top to discharge clarifled water into an external launder 22. An adjustable weir and chute 23 discharges the very fine silt. Weir 23 is immediately above the line A"-A" marking the upper limit of coarse silt supported in water by the buoyancy of coarse silt floating in the fluid mass below the line B'B.

Weir and chute 24 discharges coarse silt with the water in which it is supported.

Conduit 26 and weir and chute 25 discharge fluid medium.

The excess water delivered with the dilute feed assists in raising the coarse silt to and discharging it through weir and chute 24.

This separator discharges separately clarified water, fine silt, coarse silt and fluid medium free from coal silt.

The weirs 23, 24, and 25 may be made adjustable by gates or other types of valves in common use for controlling the flow through submerged weirs.

In the drawing the feed in Figs. I and II is shown as introduced below the line B'--B', but as illustrated in Fig. III it maybe introduced above the line B'-B' directly into the water zone as illustrated by conduit 11", which diagrammatically is intended to represent any form of conduit or chute by which the feed can be introduced directly into either the bottom or top of the water superposed above the line B'-B'.

The maximum height to which water can be raised by the pressure at the base of the conduits 11, 11', and 11" is indicated by the letters W-L; the drawing shows this conduit extends upwardly above this water line; the coal pocket and chute 9 and feed gate 10 of Fig. I; the thickener and spigot 9' and valve 10 of Fig. II and the hopper at the top of conduit 11" in Fig. III are all at an appreciable height above this water line, so that feed dropping into conduits 11, 11 and 11" will attain a relatively high velocity before plunging into the water in said conduits imparting a downward movement to said water and thus set up oscillations in said columns of water which will assist in agitating the contents of the receptacles 1, 1 and 1" and 2, 2 and 2".'

Among the new and useful results secured by my invention are: the removal of coal from the separator without removing therewith the sand or other solid constituent of the separating medium; reduction of breakage of coal caused-by passing it over screens to remove sand therefrom; reduction of the wear on screens caused by passingsand over and through them; reduction in cost of power, and wear and tear on sand handling equipment; reduction in loss of sand per ton of coal cleaned, and increased efliciency by recleaning it after its flotation by the fluid medium and before its final discharge, thus effecting more thorough removal of refuse and the production of a more valuable product.

Clogging of the feed conduits may be prevented by periodic opening and closing of the feed gate or valve, a relatively small quantity of feed being dropped into the conduit quickly at each opening of the gate. This'establishes an oscillatory motion to the column of water in the conduit, each downward stroke thereof forcing into the receptacle material in the lower part of the conduit. The same result can be obtained by raising and lowering the conduit.

The downward stroke of such pulsations feeds material into the separating zone, and also imparts an upward thrust to the separating medium and the lighter materials floating therein, thus tending to keep the floating material alive and prevent impacting thereof by the upward thrust of the buoyant material reacting against the downward thrust of the supported materials.

Figure III may be equipped with agitators of the type shown by either Figures II or I and may be provided with means for removing coarse sand or other heavy material accumulating in the lower part of the receptacle by the trapping device shown by Figure I, or other type of outlet. As the material intended to constitute the feed for Figure III is a mixture of water, sand and fine particles of coal containing no heavier or coarser material, a valved outlet can be used for emptying the receptacle. The lower part of the receptacle may have inlets for introducing water under pressure as shown in Figure II.

In the drawing the type of agitator driven from above the receptacle and/or the interlocking gate discharge through a refuse chamber as shown by Fig. I may both be substituted in an apparatus such as that shown by Fig. II, by re- Fig. H and substituting therefor a feeding device such as that shown by either Fig. I or III, thus adapting the apparatus of Fig. II to separate coarse materials as well as intermixed finer materials.

In this specification and the claims hereof, the words liquid and "water are used interchangeably to include any liquid suitable for use and the terms sand and comminuted solids" to include non-colloidal particles of any natural or artificial products, substantially insoluble in the liquid used and have specific gravities suitable for use as the solid component of fluid mediums of the described type.

I claim:

1. In a method for separating materials of differing specific gravities in which separation is effected by a maintained suspension in liquid of comrninuted solids heavier than said liquid and substantially insoluble therein having a specific gravity greater than the lighter and less than the heavier of said materials, the improvement which consists in providing a body of a suspension of the described type, in introducing materials to be separated therein, in causing the heavier of said materials to fall therethrough to the lower part of said body, in causing said lightenmaterials to accumulate in said medium and to float therein in causing the buoyancy of said accumulation to impart an upward motion of translation thereto, in continuingto feed said materials into said suspension until the buoyancy and upward movement of said lighter floating materials forces the upper portion thereof into the atmosphere above T said medium and the fluid constituent thereof, whereby said lighter materials are discharged free from both solid and liquid constituents thereof except such film of liquid as by surface tension may adhere to each particle thereof.

racemes 2. In a method for separating heavier from lighter materials by a fluid separating medium of the described type, the improvement which consists in providing a. body of fiuid medium of the described type the lower portion of which has a density greater than that ofsaid lighter materials and less than that of said heavier materials, in causing increased velocity of upward flow of the liquid constituent of said fluid medium in said upper portion which has a density less than that of said lighter materials, in causing accumulated lighter materials in said lower portion to rise to and through said upper portion of. lower specific gravity than said lighter materials to assist in supporting said accumulated lighter materials therein, in causing the combined buoyancy oi the supported and supporting accumulated materials to impart a movement oi upwind translation to the accumulated mass and in causing such movement to raise the top of said accumulation into the atmosphere, free from both. solid and liquid constituents of said medium.

3. Apparatus for separating materials of difiering specific gravities comprising in combination a receptacle adapted to contain a maintained 1% suspension of the described type, said receptacle being provided with means for maintaining the water level at a substantial distance below"- the top of said receptacle and also means for main taining the top of the said maintained suspension 1W5 at a definite level therein, a body of such suspen sion in said receptacle, means for agitating said body and also for agitating lighter materials floating in said body, whereby the buoyancy of said accumulation forces the upper part of said acm cumulation to discharge into the atmosphere above the top of said suspension and above the top of the water.

smear M. CHANGE,

Kilt) ice 7 

